Cognitive Sequelae of Adjuvant Endocrine Therapy for the Treatment of Breast Cancer in Older Women

Inclusion Criteria:

* Postmenopausal female, age 65 and older
* No more than 14 weeks post surgical resection for early stage histologically confirmed hormone receptor positive (HR+) breast cancer (BC) (i.e., Tumour size 1-2, Node status 0-1, Metastasis 0). HR+ BC defined as \>1% positive cell staining
* Prescribed either tamoxifen, letrozole, or anastrozole
* Fluent in written and spoken English; \>grade 5 education; can read large print (with or without correction); can hear normal conversation (with or without a hearing aid)
* Capacity to provide informed consent

Exclusion Criteria:

* Initiated adjuvant ET more than one week before baseline assessment
* Chemotherapy (neoadjuvant or adjuvant)
* More than one treatment of radiotherapy before baseline assessment
* Hormone replacement therapy use 4 weeks prior to baseline assessment
* Previous breast cancer or metastatic disease or other malignancy, other than any cancers treated for cure \>5 years ago and not having recurred except non-melanoma skin cancers; previous chemotherapy; previous use of selective estrogen receptor modulators (SERM) or aromatase inhibitor (AI); distant metastases
* History of or active known CNS disease (e.g. known diagnosis of stroke, Parkinson's), medical condition impairing cognitive function, including active treatment with medication known to affect cognition, or signs of cognitive impairment on the Memory Impairment Screen
* History or active known diagnosis of major psychiatric disorder in the last 10 years including bipolar disease, schizophrenia, major depression or self-reported hospitalization for psychiatric illness, alcoholism, or history of alcohol or drug abuse
* Life expectancy less than two years, acutely ill or delirious